1. Field of the Invention
The present invention relates to a drive control circuit of a charged pump circuit for raising a voltage inside an LSI in a semiconductor integrated circuit, and more particularly to a drive control circuit of a charged pump circuit for inhibiting an increase in consumed current caused by an excess of ability of the charged pump at the time of an increase in the voltage of an operating power source of the LSI and, at the same time for compensating for a reduction in the ability of the output of the increased voltage of the charged pump at the time of a reduction in the operating power source.
2. Description of the Related Art
No related art has been found which describes a technique with respect to a charged pump circuit which increases the voltage inside an LSI in a semiconductor integrated circuit, or a technique for preventing an increase in the consumed current caused by an excess of ability of the charged pump at the time of an increase in the operating power source voltage and compensating for a reduction of output ability in the increased voltage of the charged pump at the time of a reduction in the operation power source voltage.
FIG. 12 shows a structure of a general charged pump circuit. In FIG. 12, NMOS diodes ND1 through NDn (n is an integer) and NDout are connected in series between an input terminal 100 and an output terminal 200. To each of the nodes N1 through Nn of the NMOS diodes ND1 through NDn, one end of n capacitors C1 through Cn is connected respectively. To the other end of the capacitor C(2(mxe2x88x921)+1) (m less than n and m is an integer not less than 1) out of n capacitors C1 through Cn, a clock Ø1 is supplied via inverters INV1, INV3, . . . INV(nxe2x88x921).
Furthermore, a clock Ø2 is supplied to the other end of the capacitor C(2m) via inverters INV2, INV4, . . . , INVn.
Furthermore, a power source voltage VDD is applied to the input terminal 100. As shown in FIG. 13B, clocks Ø1 and Ø2 are clock signals which change in levels in a compensating manner at a timing at which high level periods do not overlap each other. The amplitude thereof is the VDD. The operation of the charged pump circuit shown in FIG. 12 will be briefly explained. When the threshold voltage of NMOS diodes ND1 through NDn and ND out is set to VD, the potential of node 1 is set to VDDxe2x88x92VD when the clock Ø1 is on a low level. When the clock Ø1 is on a high level and the clock Ø2 is on a low level, current flows from the node N1 to the node N2, from the node N3 to the node N4, . . . , and from the node N(nxe2x88x921) to the node Nn, and the potential of the node N(2m) becomes higher than the potential of the node N(2m+1) by the threshold voltage VD of the NMOS diode (for reference, m is either 0 or an integer not less than 1).
Next, when the clock Ø1 falls to a low level, the potentials of the nodes N1, N2, . . . , N2m, . . . , Nn tend to fall by the amount of the VDD because of the coupling of capacitors. However, current is supplied from the left side, and the potentials are raised to a higher level than when the clock Ø1 was previously on a low level. Next, when the clock Ø2 is raised to a high level, a current is supplied from the node N(2mxe2x88x921) to the node N(2m). When the clock Ø2 is brought back to the low level, a current is supplied from the node N(2mxe2x88x922) to the node N(2mxe2x88x921) so that the potential of the node N(2mxe2x88x921) is raised to a higher level than the potential thereof at the time of the previous cycle.
When the capacity of the capacitors C1 through Cn is denoted by C, the frequency of the clocks Ø1 and Ø2 is denoted by f, the output amplitude voltage of the inverters INV1 through INVn is denoted by VDD, and the output average current value at an output terminal 200 of the charged pump circuit is denoted by Iout, the potential of each node is raised by the amount (VDDxe2x88x92VDxe2x88x92Iout/(Cxc2x7f)) as shown in FIG. 13A as compared with the potential of the node by the adjacent input terminal 100. Here, Iout/(Cxc2x7f) denotes a charging and discharging voltage in the capacitors C1 through Cn. In other words, since the output voltage Vout at an output terminal of the charged pump circuit shown in FIG. 12 is raised by the amount (VDDxe2x88x92VDxe2x88x92Iout/(Cxc2x7f)) for each one step of the NMOS diode, the following mathematical formula is established.
Vout=VDD+nxc2x7(VDDxe2x88x92VDxe2x88x92Iout/(Cxc2x7f))xe2x88x92VDxe2x80x83xe2x80x83(1)
The average consumed current IDD of this charged pump circuit excluding a through current of the inverters (consumed current at the time of ON and OFF inside the inverters) is the sum total of the current values at which each of the inverters INV1 through INVn charges and discharges the capacitors C1 through Cn at the output average current value Iout, and the following mathematical formula is established.
IDD=nxc2x7Ioutxe2x80x83xe2x80x83(2)
In order to set the output voltage Vout at the output terminal 200 to a constant level, the output average current value Iout 1 of the charged pump circuit becomes equal to the sum total of the output average current value Iout and a Zener current Iz in the case where Zener diodes ZD 1 and ZD 2 are connected between the output terminal 200 and an earth as shown in FIG. 14. If the output voltage of the charged pump circuit shown in FIG. 14 which circuit is clamped at the Zener diodes ZD 1 and ZD 2 is denoted by Vz, the following mathematical formula is established.
Vz=VDD+nxc2x7(VDDxe2x88x92VDxe2x88x92(Iout+Iz)/(Cxc2x7f))xe2x88x92VD=Voutxe2x88x92nxc2x7Iz/(Cxc2x7f)xe2x80x83xe2x80x83(3)
From the mathematical formulae (1), (2) and (3), the Zener current Iz, and the average consumed current IDD is established in the following manner.
xe2x80x83Iz=(Voutxe2x88x92V z)/nxc2x7Cxc2x7fxe2x80x83xe2x80x83(4)
IDD=nxc2x7(Iout+Iz)xe2x80x83xe2x80x83(5)
When the output average current value Iout is at a constant level, the output voltage Vout increases as seen from the mathematical formula (1) at the time when the power source voltage VDD increases, and the Zener current Iz and the average consumed current IDD increase according to the mathematical expressions (4) and (5). FIGS. 15A and 15B show operating waveforms of a charged pump circuit having the structure shown in FIG. 14.
In a conventional charged pump circuit, since the number of steps of the NMOS diodes, namely the number of steps n of the charged pump circuit and the capacity C of the capacitors (1xe2x88x92Cn) which are connected to each of the nodes of the NMOS diodes, are fixed values which are determined at the time of the circuit design, there arises a problem that an unutilized Zener current Iz which flows to the Zener diodes for use in the output voltage clamp increases and the average consumed current IDD of the inverters increases with an increase of the power source voltage VDD in the case where the output average current value Iout of the charged pump circuit is constant.
The present invention has been made in view of the aforementioned circumstances, and an object of the present invention is to provide a drive control circuit of a charged pump circuit which circuit is capable of inhibiting an increase of the average consumed current IDD of the inverters at the time of the increase in the power source voltage VDD in the case where the output average current value Iout is constant.
In order to attain the aforementioned object, according to a first aspect of the present invention, there is provided a drive control circuit of a charge pump circuit having:
a plurality of diodes connected in series between an input terminal and an output terminal;
a plurality of capacitors one end of each of which is connected to each node of said plurality of diodes and to the other end of each of which is supplied a clock signal;
Zener diodes for use in an output voltage clamp connected between said output terminal and an earth; wherein said drive control circuit of a charge pump circuit has a plurality of drive steps which raise the power source voltage supplied to said input terminal to a predetermined voltage by supplying two types of clock signals which change levels in a compensating manner so that high level periods do not overlap each other to each of said other terminals of adjacent capacitors in each of said plurality of capacitors and then output the power source voltage, and said drive control circuit of a charge pump circuit comprises:
a power source voltage detecting circuit for detecting said power source voltage;
a control circuit for changing the number of drive steps of said charge pump circuit in accordance with the output detected by the power source voltage detecting circuit; and
a by-pass circuit for allowing the final output of the drive steps to be by-passed towards said output terminal in accordance with the change in the number of drive steps.
According to the first aspect of the present invention, the power source voltage VDD is detected with the power source voltage detecting circuit, the number of the drive steps of the charged pump circuit is changed by the control circuit in accordance with the detected output of the power source voltage VDD, and the output of the last step of the drive steps can be allowed to be by-passed towards the output terminal of the charged pump circuit in accordance with the change in the number of drive steps of the charged pump circuit by the by-pass circuit with the result that the number of drive steps of the charged pump circuit can be changed in accordance with increases and decreases in the VDD voltage.
Consequently, in the case where the output average current (load current) value Iout is constant as in the conventional charged pump circuit, it is possible to inhibit an increase in unutilized Zener current Iz which flows through the Zener diodes for use in the output voltage clamp at the time of an increase in the power source voltage VDD, and to inhibit an increase in the average consumed current IDD as a result of an increase in this Zener current Iz.
According to a second aspect of the present invention, there is provided a drive control circuit of the charge control circuit having:
a plurality of diodes connected in series between an input terminal and an output terminal;
a plurality of capacitors one end of each of which is connected to each node of said plurality of diodes and to the other end of each of which is supplied a clock signal;
Zener diodes for use in an output voltage clamp connected between said output terminal and an earth; wherein said drive control circuit of a charge pump circuit has a plurality of drive steps which raise the power source voltage supplied to said input terminal to a predetermined voltage by supplying two types of clock signals which change levels in a compensating manner so that high level periods do not overlap each other to each of said other terminals of adjacent capacitors in each of said plurality of capacitors and then output the power source voltage, and said drive control circuit of a charge pump circuit comprises:
a current detecting circuit for detecting current flowing to said Zener diodes;
a control circuit for changing the number of drive steps of said charge pump circuit in accordance with the output detected by the power source voltage detecting circuit; and
a by-pass circuit for allowing the final output of the drive steps to be by-passed towards said output terminal in accordance with the change in the number of drive steps.
According to the second aspect of the present invention, there is provided a current detecting circuit for detecting current flowing through the Zener diodes for use in the output voltage clamp connected between the output terminal of the charged pump circuit and the earth, the control circuit for changing the number of drive steps of the charged pump circuit in accordance with the detected output of the current detecting circuit, and the by-pass circuit for allowing the output of the last step of the drive steps to be by-passed towards the aforementioned output terminal in accordance with the change in the number of drive steps with the result that the number of drive steps of the charged pump circuit can be changed in accordance with increases and decreases in the Zener current Iz which flows through the Zener diodes for use in the output voltage clamp.
Consequently, in the case where the output average current (load current) value Iout in the conventional charged pump circuit is constant, it is possible to inhibit an increase in unutilized Zener current Iz which flows through the Zener diodes for use in the output voltage clamp at the time of an increase in the power source VDD, and to inhibit an increase in the average consumed current IDD as a result of an increase in this Zener current Iz.
Furthermore, according to the second aspect of the invention, since the unutilized Zener current Iz which flows through the Zener diodes for use in the output voltage clamp is detected with a current detecting circuit, and the number of drive steps of the charged pump circuit is changed in accordance with increases and decreases in the Zener current Iz, it is possible to prevent unutilized Zener current from increasing along with the change in the output average current (load current) value Iout in the charged pump circuit, and to prevent the average consumed current IDD from increasing as a result of an increase in this Zener current Iz.
According to a third aspect of the present invention, there is provided a drive control circuit of a charge pump circuit having:
a plurality of diodes connected in series between an input terminal and an output terminal;
a plurality of capacitors one end of each of which is connected to each node of said plurality of diodes and to the other end of each of which is supplied a clock signal;
Zener diodes for use in an output voltage clamp connected between said output terminal and an earth; wherein said drive control circuit of a charge pump circuit has a plurality of drive steps which raise the power source voltage supplied to said input terminal to a predetermined voltage by supplying two types of clock signals which change levels in a compensating manner so that high level periods do not overlap each other to each of said other terminals of adjacent capacitors in each of said plurality of capacitors and then output the power source voltage, and said drive control circuit of a charge pump circuit comprises:
a power source voltage detecting circuit for detecting said power source voltage;
a control circuit for changing the number of drive steps of said charge pump circuit in accordance with the output detected by the power source voltage detecting circuit; and
a by-pass circuit for allowing said power source voltage to be by-passed in such a manner as to be supplied to the input side of the first step of the drive steps in accordance with the change in the number of drive steps.
According to the third aspect of the present invention, since the present invention has a control circuit for changing the number of drive steps of the charged pump circuit in accordance with the detected output of the power source detecting circuit, and the by-pass circuit for allowing the power source voltage to be bypassed so that the power source voltage is supplied to the input side of the first step of the drive steps in accordance with the change in the number of drive steps of the charged pump circuit with the result that the number of drive steps of the charged pump can be changed in accordance with increases and decreases of the power source voltage.
Consequently, in the case where the output average current (load current) value Iout is constant as in the conventional charged pump circuit, it is possible to inhibit unutilized Zener current Iz which flows through the Zener diodes for use in the output voltage clamp from increasing at the time of an increase in the power source voltage VDD, and to prohibit the average current IDD from increasing as a result of the increase in this Zener current Iz.
According to a fourth aspect of the present invention, there is provided a drive control circuit of the charge control circuit having:
a plurality of diodes connected in series between an input terminal and an output terminal;
a plurality of capacitors one end of each of which is connected to each node of said plurality of diodes and to the other end of each of which is supplied a clock signal;
Zener diodes for use in an output voltage clamp connected between said output terminal and an earth; wherein said drive control circuit of a charge pump circuit has a plurality of drive steps which raise the power source voltage supplied to said input terminal to a predetermined voltage by supplying two types of clock signals which change levels in a compensating manner so that high level periods do not overlap each other to each of said other terminals of adjacent capacitors in each of said plurality of capacitors and then output the power source voltage, and said drive control circuit of a charge pump circuit comprises:
a current detecting circuit for detecting current flowing to said Zener diodes;
a control circuit for changing the number of drive steps of said charge pump circuit in accordance with the output detected by the power source voltage detecting circuit; and
a by-pass circuit for allowing said power source voltage to be by-passed in such a manner as to be supplied to the input side of the first step of the drive steps in accordance with the change in the number of drive steps.
According to the fourth aspect of the invention, since the present invention has a current detecting circuit for detecting the current flowing through the Zener diodes for use in the output voltage clamp connected between the output terminal of the charged pump circuit and the earth, a control circuit for changing the number of drive steps of the charged pump circuit in accordance with at least one of the detected output of the current detecting circuit and the power source voltage, and a by-pass circuit for allowing the power source voltage to be by-passed in such a manner that the power source voltage is supplied to the input side of the first step of the drive steps in accordance with the change in the number of drive steps of the charged pump circuit, the number of steps of the charged pump circuit which are actually operated can be changed in accordance with increases and decreases of the power source voltage VDD.
Consequently, in the case where output average current (load current) value Iout in the conventional charged pump circuit is constant, it is possible to inhibit unutilized Zener current which flows through Zener diodes for use in the output voltage clamp from increasing at the time of an increase in the power source voltage VDD, and to inhibit the average consumed current from increasing as a result of an increase of this Zener current Iz.
Furthermore, according to the fourth aspect of the invention, since the unutilized Zener current Iz which flows through Zener diodes for use in the output voltage clamp is detected with the Zener current detecting circuit and the number of drive steps of the charged pump is changed in accordance with increases and decreases in the Zener current Iz, it is possible to prevent the unutilized Zener current Iz from increasing along with the change in the output average current (load current) value in the charged pump circuit, and to prevent the average consumed current IDD from increasing as a result of an increase in this Zener current Iz.
According to a fifth aspect of the present invention, there is provided a drive control circuit of the charge control circuit having:
a plurality of diodes connected in series between an input terminal and an output terminal;
a plurality of capacitors one end of each of which is connected to each node of said plurality of diodes and to the other end of each of which is supplied a clock signal;
Zener diodes for use in an output voltage clamp connected between said output terminal and an earth; wherein said drive control circuit of a charge pump circuit has a plurality of drive steps which raise the power source voltage supplied to said input terminal to a predetermined voltage by supplying two types of clock signals which change levels in a compensating manner so that high level periods do not overlap each other to each of said other terminals of adjacent capacitors in each of said plurality of capacitors and then output the power source voltage, and said drive control circuit of a charge pump circuit comprises:
a constant current source circuit for generating a constant current having a negative power source voltage dependency constant;
an oscillation circuit which is driven by the constant current having a negative power source voltage dependency constant generated by the constant power source circuit, for generating a pulse signal of a frequency having a negative power source voltage dependency constant; and
a clock signal supply circuit for creating said two types of clock signal on the basis of the pulse signal output from the oscillation circuit and supplying said two types of clock signal to the charge pump circuit.
According to the fifth aspect of the invention, the constant current having a negative power source voltage dependency constant is generated by the constant current source generating circuit, and a pulse signal of a frequency having a negative power source voltage dependency constant is generated, and the charged pump circuit is driven by a clock having the frequency by the clock signal supplying circuit with the result that the operating frequency of the charged pump circuit can be changed in accordance with increases and decreases in the power source voltage VDD.
Consequently, in the case where the output average current (load current) value Iout in the conventional charged pump circuit is constant, it is possible to inhibit unutilized Zener current Iz which flows through the Zener diodes for use in the output voltage clamp from increasing at the time of an increase in the power source voltage VDD, and to inhibit the average consumed current IDD from increasing as a result of an increase in this Zener current Iz.
According a sixth aspect of the invention, there is provided a drive control circuit of the charge control circuit having:
a plurality of diodes connected in series between an input terminal and an output terminal;
a plurality of capacitors one end of each of which is connected to each node of said plurality of diodes and to the other end of each of which is supplied a clock signal;
Zener diodes for use in an output voltage clamp connected between said output terminal and an earth; wherein said drive control circuit of a charge pump circuit has a plurality of drive steps which raise the power source voltage supplied to said input terminal to a predetermined voltage by supplying two types of clock signals which change levels in a compensating manner so that high level periods do not overlap each other to each of said other terminals of adjacent capacitors in each of said plurality of capacitors and then output the power source voltage, and said drive control circuit of a charge pump circuit comprises:
a current detecting circuit for detecting current flowing to said Zener diodes;
a constant current source circuit for fetching the output detected by the current detecting circuit and generating a constant current in reverse proportion to the value of the current flowing to said Zener diodes;
an oscillation circuit driven by the constant current source circuit for generating a pulse frequency of a frequency in reverse proportion to the value of the current flowing to said Zener diodes; and
a clock signal supply circuit for creating said two types of clock signal on the basis of the pulse signal output from the oscillation circuit and supplying the two types of clock signal to the charge pump circuit.
According to a sixth aspect of the invention, the current which flows through the Zener diodes for use in the output voltage clamp connected between the output terminal of the charged pump circuit and the earth is detected with the current detecting circuit; the detected output of the current detecting circuit is fetched; the constant current which is in inverse proportion to the value of the current flowing through the aforementioned Zener diodes is generated by the constant current source circuit; a pulse signal of the frequency is generated with an oscillation circuit which is driven by the constant current source circuit, the frequency being in inverse proportion to the value of the current flowing through the Zener diodes; and the two kinds of clock signals are prepared by the clock signal supply circuit on the basis of the pulse signal which is output from the oscillation circuit with the result that an operating frequency of the charged pump circuit can be changed in accordance with increases and decreases in the Zener current Iz.
Consequently, in the case where the output average current (load current) value Iout in the conventional charged pump circuit is constant, it is possible to inhibit unutilized Zener current Iz which flows through the Zener diodes for use in the output voltage clamp from increasing at the time of an increase in the power source voltage VDD, and to inhibit the average consumed current IDD from increasing as a result of the increase in this Zener current Iz.
Furthermore, according to the sixth embodiment of the present invention, since the unutilized Zener current Iz which flows through the Zener diodes for use in the output voltage clamp is detected with the Zener current detecting circuit, and the operating frequency of the charged pump circuit is changed in accordance with increases and decreases in the Zener current Iz, it is possible to prevent the unutilized Zener current Iz from increasing along with the change in the output average current (load current) in the charged pump circuit, and to prevent the average consumed current IDD from increasing as a result of the increase in this Zener current Iz.